Introduction to CDP (Cisco Discovery Protocol)

Let’s talk a bit about network management. Perhaps not the most exciting topic but I’m going to show you how you can use CDP (Cisco Discovery Protocol) to help you build network maps and what other information it can reveal.

Most networks have multiple switches and/or routers and to make our life easier it’s good to have a network map that shows us how everything is connected to each other, what kind of devices we have, to what VLAN they belong and the IP addresses that we are using. CDP is a Cisco protocol that runs on all Cisco devices that helps us discover Cisco devices on the network. CDP is Cisco proprietary, runs on the data-link layer and is enabled by default.

Let’s take a look at a network map:

Above we have 3 routers. Now if I had no idea what the network looked like we could use CDP to build the network map that you see above. Let me show you how:

Use the show cdp neighbors command to see all directly connected neighbors. Above you see that R1 is connected to R2 and you can also see the platform (3640 router) and the interfaces on both sides. Let me show you the other routers as well:

Forum Replies

I work as technical support in Internet Services & Communications company and we don’t use Cisco products only, we also use other network products from different vendors like Ubiquiti, mikrotik, Exalt, etc. and we connect all these different products with each other!!
so when I use CDP to show which devices connected to cisco switch or router I noticed that information of different vendors products also appears to me!!
My question is why I show this info ? I know that CDP is Cisco proprietary so how it’s able to identify the products from other vendors???

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